Visibility diagrams for the years when the prophet Muḥammad resided in Medina can be obtained from the following table. These may be of use to historians and theologians who wish to study the chronology of early Islam.
|0||11 0||24 Jul 621||14 Jun 622|
|1||1 12||14 Jul 622||3 Jun 623|
|2||13 24||3 Jul 623||22 May 624|
|3||25 36||21 Jun 624||12 May 625|
|4||37 48||10 Jun 625||1 May 626|
|5||49 60||31 May 626||21 Apr 627|
|6||61 72||20 May 627||10 Apr 628|
|7||73 84||9 May 628||30 Mar 629|
|8||85 96||29 Apr 629||19 Mar 630|
|9||97 108||18 Apr 630||8 Mar 631|
|10||109 120||7 Apr 631||25 Feb 632|
|11||121 132||26 Mar 632||14 Feb 633|
The months and years in these diagrams are denoted in the proleptic Islamic lunar calendar, which assumes (as in the present-day Islamic calendar) that no intercalary months were inserted during the first decade of the Islamic calendar. However, before the Farewell Pilgrimage (Dhu ʾl-Ḥijja 10 AH), when the intercalation of extra months in the Arabian calendar was abolished (Qurʾān, sūra 9:36-37), it was customary to add an extra month to the year every two or three years in order to keep the lunar calendar in step with the seasons.
As the intercalation rule of the Arabian calendar is uncertain, all proposed reconstructions of the Islamic calendar before 10 AH can only be regarded as hypothetical. For this reason, Western calendar dates commonly cited for key events in early Islam such as the hijra, the Battle of Badr, the Battle of Uhud, the Battle of the Trench and other events related to the life of Muḥammad, should be viewed with caution as they can be in error by one, two, three or more lunar months.